The capacity of a conventional multi-beam satellite or terrestrial communication system is often limited by its frequency-reuse or code-reuse capability. In such systems, the level of frequency domain channelization or code assignment over a collection of simultaneous beams is dictated by the angular separation between beams. Angular separation is needed to reduce co-channel interference through beam pattern sidelobes. The number of distinct frequency channels and code assignments over the beams is known as the frequency or code-reuse factor.
For example, a satellite communication system may employ a 12-channel or 12-code reuse scheme to realize angular separation among identical channel beams. This is done to guarantee sufficient channel rejection. This reuse level is accomplished through a 12-cell reuse configuration. As a consequence, each beam in a 12-beam configuration is capable of delivering 1/12 of the potential capacity. Achieving greater system capacity or realizing a reuse factor much lower than 12 is difficult in conventional systems because the interference produced by competing users can be rather high.
Satellite communication systems have used phased array antennas to communicate with multiple users through multiple antenna beams. Typically, efficient bandwidth modulation techniques are combined with multiple access techniques, and frequency separation methods are employed to increase the number of users. Because electronic environments are becoming increasingly dense, more sophistication is required for wireless communication systems. For example, with all users competing for a limited frequency spectrum, the mitigation of interference among various systems is a key to the allocation of the spectrum to the various systems.
Beam steering and nulling systems have been developed mostly by the military for communications and radar operations. However, such systems have been capable of only a small number of beams and a limited number of narrow nulls. One reason for these limitations is the prohibitively high computational cost of the underlying signal processing.
There is a need for a method and apparatus to increase the frequency reuse factor in communication systems. There is also a significant need for methods and apparatus for providing more efficient processing of antenna beam patterns in a communication system. In addition, these needs are especially significant for satellite communication systems which include non-geostationary satellites and geostationary satellites.